option to add additional tags file names

[wolftune]

in my case to use https://github.com/aloiscochard/codex and the file it makes called codex.tags

[segevfiner]

It will also be useful if such option supports upwards/downwards searching like Vim supports. This is useful when you have tags files in sub directories of the project. Atom does have an advantage here that it has the project root folder in hand, so upwards search might not be all that useful.